This invention relates to semiconductor lasers and particularly to semiconductor injection lasers manufactured from II/VI materials and operating in the blue-green region.
Semiconductor lasers comprised of III/V materials operating in the red and infrared regions are commonly found in optical data storage applications. If laser devices operating at shorter wavelengths such as green, blue/green and blue were available, the data storage density of optical data storage devices could be increased. However, practical semiconductor laser diodes operating at the shorter wavelengths have not as yet been manufactured. The prior art has focussed on a variety of means for utilizing II/VI materials to provide shorter wavelength semiconductor lasers.
Blue-green II/VI semiconductor injection lasers have been produced by Haase, et al. ("Blue-Green Laser Diodes", Appl. Phys. Lett. 59 (11), 9 Sep. 1991) using a separate-confinement heterostructure (SCH) configuration. These lasers have ZnS.sub.0.06 Se.sub.0.94 cladding layers, a ZnSe waveguiding region, and a Cd.sub.0.2 Zn.sub.0.8 Se quantum-well active region. Although this structure has provided room-temperature pulsed and low-temperature continuous operation, it has the disadvantage that it cannot be grown with all layers pseudomorphic to the GaAs substrate. Pseudomorphic lasers can be made without separate confinement, by omitting the ZnSe guiding region, but additional quantum wells are required to compensate for the reduction in optical confinement. Consequently, the threshold current density increases. Also, the improvement in optical confinement obtained by additional quantum wells is limited, because the large lattice mismatch (about 1.5%) between Cd.sub.0.2 Zn.sub.0.8 Se and ZnS.sub.0.06 Se.sub.0.94 limits the total thickness of Cd.sub.0.2 Zn.sub.0.8 Se.
Growth of Zn.sub.1-x Mg.sub.x S.sub.y Se.sub.1-y materials by MBE has been demonstrated by Okuyama, et al (Jap. J. App. Phys. 30, L1620 (1991)). They have implemented Zn.sub.1-x Mg.sub.x S.sub.y Se.sub.1-y cladding layers in optically pumped lasers operating at temperatures up to 500K and in 77K multi-quantum-well p-n injection lasers without separate confinement. The use of Zn.sub.1-x Mg.sub.x S.sub.y Se.sub.1-y for II/VI lasers is also shown in U.S. patent application Ser. No. 815,686, filed Dec. 31, 1991 now U.S. Pat. No. 5,260,958 issued Nov. 9, 1993.
The present invention is directed to a blue-green II/VI separate confinement semiconductor injection laser utilizing a Zn.sub.1-u Cd.sub.u Se active layer (quantum well) having Zn.sub.1-x Mg.sub.x S.sub.y Se.sub.1-y cladding layers and ZnS.sub.z Se.sub.1-z guiding layers and a GaAs substrate. The devices are operable in a pulsed mode at room temperature. The use of quaternary Zn.sub.1-x Mg.sub.x S.sub.y Se.sub.1-y cladding layers permits both lattice matching of all layers, and an increase of the cladding and guiding layer band-gaps. Thus, lasers can be made with improved electrical and optical confinement. Alternatively, the band-gap of the active region may be increased to yield lasing at shorter wavelengths (u=0).